Ghost notes...

  • Thread starter Thread starter Fusioninspace
  • Start date Start date
F

Fusioninspace

New member
Every now and then when I'm playing with our worship team, I'll hear what I call Ghost notes. It's like everyone's playing their part, and then it's like some individual tone will jump out of the mix - it could be a single note or even some kind of melody. And it almost sounds like a "pure" tone - like a chime of a bell sort of ring to it. As I look around I don't see anyone doing anything that looks like they are playing that particular single note...

Is this a physics/acoustics thing where if we're all playing the same chord with different instrument, somehow something comes together and creates this new tone/note? Because it's in key and in tune with us, it makes me think it might be somekind of standing wave/harmonic - except its a much higher frequency than what I would call a standing wave related to low frequencies.

At times, it sounds like something from the original recording that we don't happen to be playing (like an occasional fill) - So it could be something in my head... Maybe it's God telling me I need to work on my solo stuff :rolleyes:

Any thoughts?????
 
when in doubt, blame the keyboard player!



I've actually experienced that or something similar, when you swear you could hear a part played, but no one's playing it. I think that when the music is sufficiently loud, my mind either fills in the blanks or maybe it is some sort of combined wave effect.
 
Fusioninspace said:
Every now and then when I'm playing with our worship team, I'll hear what I call Ghost notes. It's like everyone's playing their part, and then it's like some individual tone will jump out of the mix - it could be a single note or even some kind of melody. And it almost sounds like a "pure" tone - like a chime of a bell sort of ring to it. As I look around I don't see anyone doing anything that looks like they are playing that particular single note...

Is this a physics/acoustics thing where if we're all playing the same chord with different instrument, somehow something comes together and creates this new tone/note? Because it's in key and in tune with us, it makes me think it might be somekind of standing wave/harmonic - except its a much higher frequency than what I would call a standing wave related to low frequencies.

At times, it sounds like something from the original recording that we don't happen to be playing (like an occasional fill) - So it could be something in my head... Maybe it's God telling me I need to work on my solo stuff :rolleyes:

Any thoughts?????
Click to expand...

Harmonics can induce the brain to hear notes that aren't there. Pick up an in-tune acoustic guitar and play a first position D chord, except mute the top string so the F# doesn't ring. Usually you will "hear" the 9th (high E) in there even though no string is ringing with that pitch.
 
Fusioninspace said:
Is this a physics/acoustics thing
Click to expand...

Back in my college days in an Acoustics course, we learned about ghost tones, which are essentially difference frequencies produced when two tones of differing frequencies are played together. In a classroom demo, we played recordings of two flute notes being played together - flute being selected because its natural waveform is the nearest thing in an instrument to a pure sine wave. A spectrum analyzer attached to the output of the tape player proved that only the two tones were there in the audio output. Yet all of us distinctly heard the third (ghost) tone. What I don't recall is whether the the mixing that produced the ghost tone was an acoustics thing (tone produced during sound propogation in the room) or mental thing (tone produced in your brain due to something -- maybe the non-linear characteristics of huma hearing).

Tom
 
Oancient1 said:
Back in my college days in an Acoustics course, we learned about ghost tones, which are essentially difference frequencies produced when two tones of differing frequencies are played together. In a classroom demo, we played recordings of two flute notes being played together - flute being selected because its natural waveform is the nearest thing in an instrument to a pure sine wave. A spectrum analyzer attached to the output of the tape player proved that only the two tones were there in the audio output. Yet all of us distinctly heard the third (ghost) tone. What I don't recall is whether the the mixing that produced the ghost tone was an acoustics thing (tone produced during sound propogation in the room) or mental thing (tone produced in your brain due to something -- maybe the non-linear characteristics of huma hearing).

Tom
Click to expand...

Beat frequencies - the same as you use to tune by ear - are produced by positive and negative reinforcement of two waveforms and are the difference between the two, i.e., if you play a 440Hz tone and a 441Hz tone, you will hear a 1Hz beat frequency. It's why chords sound the way they do to us; if you play a 440 and a perfect 5th above it, a 660, then it creates a 220Hz beat frequency, which is an octave below the root. Add a third and it beats against the 1 and the 5, creating still more beat frequencies, so that we hear a much more complex set of tones than just the three that are playing.
 
Oancient1 said:
Back in my college days in an Acoustics course, we learned about ghost tones, which are essentially difference frequencies produced when two tones of differing frequencies are played together. In a classroom demo, we played recordings of two flute notes being played together - flute being selected because its natural waveform is the nearest thing in an instrument to a pure sine wave. A spectrum analyzer attached to the output of the tape player proved that only the two tones were there in the audio output. Yet all of us distinctly heard the third (ghost) tone. What I don't recall is whether the the mixing that produced the ghost tone was an acoustics thing (tone produced during sound propogation in the room) or mental thing (tone produced in your brain due to something -- maybe the non-linear characteristics of huma hearing).

Tom
Click to expand...
The experiment produced the result that was expected. In this case it would partly be down to psycho acoustics. Interestingly when this experiment is carried out with two pure sine waves the results are less predictable. You are less inclined to hear the "absent" third, fifth, whatever. There are sound reasons why this might be expected.


A flute will produce a reasonably pure tone in relation to a sine wave. Closer than say a plucked, hammered or bowed string. The reason for this is the manner in which the air is being moved. A closed pipe produces a good note without the need for a secound system to drive the air such as a soundboard on the enclosure of a guitar body. violin body or piano. The tone of any instrument is a result of the harmonic frequencies that are being produced on top of the fundamental frequencies. These frequencies are a result of many things. The foremost being the properties of the material that the instrument is made of. The brain is exaggerating the amplitude and possibly the purity of these harmonic frequencies. Psych acoustic is a nightmare to conclusively study with any certainty..

On a side note the purest or closest tone to a sine wave would be that produced by a tuning fork. That is if you exclude tones created from electronic synthesized equipment which are capable of producing a pure sine wave.

Interesting experiment.
 
ggunn said:
Beat frequencies - the same as you use to tune by ear - are produced by positive and negative reinforcement of two waveforms and are the difference between the two, i.e., if you play a 440Hz tone and a 441Hz tone, you will hear a 1Hz beat frequency. It's why chords sound the way they do to us; if you play a 440 and a perfect 5th above it, a 660, then it creates a 220Hz beat frequency, which is an octave below the root. Add a third and it beats against the 1 and the 5, creating still more beat frequencies, so that we hear a much more complex set of tones than just the three that are playing.
Click to expand...
Sorry to be pedantic but what temparement are we talking about because a "perfect fifth" in relation to thirds, fourths and octaves etc, is not available to us in 12 tone equal temperament tuning (12 TET). OK so the fifth in 12 TET is only a couple of cents off but the thirds and fourths get Muddy. Can you clarify the point you are making? Are you saying that the psycho acoustic effect of hearing "ghost" tones is a result of frequency discrepancies between pure intervals and the adjusted intervals in equal temperament tuning? Or that chords in 12 TET are prone to fool the brain more than Just or pure temparaments?
 
jfrog said:
when in doubt, blame the keyboard player!



I've actually experienced that or something similar, when you swear you could hear a part played, but no one's playing it. I think that when the music is sufficiently loud, my mind either fills in the blanks or maybe it is some sort of combined wave effect.
Click to expand...
It's near impossible to give some pointers for further investigation without some more info. What instruments, venue type, is it the same with a full room as opposed to an empty room? Also some idea of how often and in what keys, minor or major would be good even better would be what interval the ghost tone is? Sounds like a psycho acoustic trick to me but there are other possibilities depending on the circumstance.
 
i've noticed several people on gearslutz mention this same phenomenon, in the "stupidest thing you've ever heard during a session" thread

it's one of those things that seems to occur often enough that i would assume that it exists...and i would also probably attribute it to the interplay between the harmonics of the different instruments, but who really knows

oddly enough, most of the people on GS who mentioned experiencing this had it happen when working on gospel/worship music...
 
If you are hearing a tone that is higher in pitch than a fundamental you are playing, that's just a harmonic of the fundamental. If you are hearing a lower pitch (or higher, but they can be tougher to spot), that results from two higher pitches being played, that is an intermodulation (IM). The effect is well known in pipe organs where by creating a stop that plays a first and fifth together, it creates the lower octave as a IM (called a 'resultant'). IM is normally much lower in amplitude than the fundamental, so it is also partly a psychoacoustic effect. But it is not merely that, it can indeed be measured acoustically.

Temperament is not too important; the IM pitch will be created based upon the two tones, whatever they are. The IM might not be in pitch, but for bass notes pitch is not well perceived anyway.
 
Oh it exists for sure and it can be down to a few things.

Wolf tones - Something with a natural frequency of vibration is excited by a certain frequency. In other words a room, an object or anything that will move is set into motion at a frequency that it naturally want to vibrate at. The cause is normally another sound wave of the same frequency. A crude amplifier in effect.

Psycho acoustic phenomenon -The part of the brain that processe audio is just as capable of being fooled into believing something is going on when it's not just as an optical illusion can fool your eyes.

There can also be a combination of the two.
 
mshilarious said:
If you are hearing a tone that is higher in pitch than a fundamental you are playing, that's just a harmonic of the fundamental. If you are hearing a lower pitch (or higher, but they can be tougher to spot), that results from two higher pitches being played, that is an intermodulation (IM). The effect is well known in pipe organs where by creating a stop that plays a first and fifth together, it creates the lower octave as a IM (called a 'resultant'). IM is normally much lower in amplitude than the fundamental, so it is also partly a psychoacoustic effect. But it is not merely that, it can indeed be measured acoustically.

Temperament is not too important; the IM pitch will be created based upon the two tones, whatever they are. The IM might not be in pitch, but for bass notes pitch is not well perceived anyway.
Click to expand...
I'm not sure that this has to do with intermodulation although it could be. IM is less common in physical models than in radio or electronic environments. It would help to know more about the frequency relationship as IM is generally non linear. Temprement can make a difference with regard to IM and it's effect but again I don't think it would apply here.
 
Wow, I really want to thank everyone for their comments! I thought I was going nuts - I started to mention in a few times after we played... but reason got the best of me and I kept my mouth shut.

Now it looks like there is some kind of valid explanation for this to happen.

Thanks again! :D
 
muttley600 said:
Sorry to be pedantic but what temparement are we talking about because a "perfect fifth" in relation to thirds, fourths and octaves etc, is not available to us in 12 tone equal temperament tuning (12 TET). OK so the fifth in 12 TET is only a couple of cents off but the thirds and fourths get Muddy. Can you clarify the point you are making? Are you saying that the psycho acoustic effect of hearing "ghost" tones is a result of frequency discrepancies between pure intervals and the adjusted intervals in equal temperament tuning? Or that chords in 12 TET are prone to fool the brain more than Just or pure temparaments?
Click to expand...

I didn't mean anything nearly so rigorous. When you play any two different tones, there is a beat frequency generated whose frequency is the difference between the two tones. When they are far apart enough (i.e., for a note and its fifth, the beat frequency is an octave below the lower note), they can contribute to the sense of a chord. With a perfect fifth (which is accessible on a tunable instrument like a guitar) it's exactly that subharmonic, and in a tempered instrument, the closer the harmonic relationship (i.e., the closer around the circle of fifths, i.i.e.e., the less the tempering difference from a perfect interval) the closer the beat wavelengths are to exact multiples of those of the notes played.

I worked out some of these relationships some years ago, and I remember the 1 and 5 generating a beat frequency an octave below the 1, and I believe that the beat frequency of the 1 and the maj 3rd is two octaves below the 1. In a major triad, the 1 beats against the 5 and the 3, and the 5 and the 3 beat against each other. Beat frequencies also beat against each other, although as the order of the effect increases, the amplitude decreases.

Someone else mentioned intermodulation; perhaps that is the correct term to describe it. When I saw it on oscilloscope screens in engineering school, we called it aliasing.
 
God Is A Lie! Baba Booey Baba Booey Baba Booey Baba Booey Baba Booey Baba Booey Baba Booey Baba Booey Baba Booey Baba Booey Baba Booey Baba Booey Baba Booey Baba Booey Baba Booey *scuttles Out Of Thread*
 
Yes I think what your describing is more to do with intermodulation or in terms of the acoustics of organ pipes is termed the "Resultant". Mshilarious put forward this posiblility and it's a credible explanation for what might be going on.

A brief hunt for a good explanation online and I found this.

With regard to the effect of temperament and resultants it has this to say.

In many cases both pitches are taken from the same rank of pipes, a fifth apart, as a further cost-saving measure. Because 5ths in the equal-tempered scale are not perfect fifths, the resultant tones will not be quite in tune, but it works because the human ear does not hear such low tones with enough accuracy to tell the difference.
Click to expand...
which is true but the higher the frequency the more critical it becomes. My only problem with this here is that it's not a common chance occurrence in normal musical situations, it could be though. Choral music is another place where it can be heard.
 
You must log in or register to reply here.
Back
Top